Basement membrane (BM) disease is the major life-threatening complication of diabetes mellitus, the third leading cause of death in the United States today. In an effort to shed some light on the pathogenesis of BM changes in diabetes, we propose to study normal and diabetic isolated BM from several points of view. Renal tubules are known to be affected by diabetic BM disease and also are easily dissociated from kidneys in pure form. We propose to isolate ultrastructurally pure tubule BM for analyses. This BM is particularly well-suited to our study because: a) It is morphologically pure and structurally defined, b) it is tissue-specific, c) it can be isolated in quantities adequate for biochemical analyses, and d) renal tubules are readily grown in culture and produce BM and BM collagens similar to those isolated from tubule BM in vivo. With these considerable advantages, we will carry out the following experiments: a) Analyses of renal tubule BM by experimental ultrastructural techniques to further clarify regional dissimilarities shown by us to be present within a single BM, and to assess macromolecular architectural differences between normal and diabetic BM, b) Biochemical characterization of heterogeneous collagen peptides which we have identified in tubule BM, c) Morphological and biochemical analyses of BM and BM collagen biosynthesis in renal tubules from normal and diabetic animals in vitro, and d) long-range plans include in vitro BM biosynthesis studies which could be controlled by nutritional or hormonal factors (e.g. glucose, somatotropin, insulin, etc.) to induce changes that may simulate those observed in vivo. It is hoped that these studies will provide insights into the nature of BM alterations in diabetes. We believe that when these are clarified and the parameters surrounding the pathogenesis of the disorder are more fully understood, the possibility of elucidating its causes will be within reach. This could lead ultimately to positive therapeutic intervention in the progression of diabetic BM disease.